Currently, magnetoresistance (MR) heads are currently used in read heads or for reading in a composite head. MR heads use a MR sensor in order to read data that has been stored in magnetic recording media. Giant magnetoresistance (“GMR”) has been found to provide a higher signal for a given magnetic field. GMR is based on spin dependent scattering at magnetic interfaces. Spin dependent scattering at interfaces is described in an article by S. Parkin in 71 Phys. Rev. Let. P. 1641 (1993).
Conventional MR sensors which utilizes GMR to sense the magnetization stored in recording media typically include at least two magnetic layers separated by nonmagnetic layer. The magnetization of one of the magnetic layers is free to rotate in response to an external magnetic field. This magnetic layer is known as the free layer. The magnetization of the other magnetic layer is fixed in place, typically using an antiferromagnetic (“AFM”) layer. This magnetic layer is known as the pinned layer. For the purposes of this disclosure, this physical structure will be termed a conventional spin valve. However, as discussed below, current can be driven through the conventional spin valve in different directions. The conventional spin valve may also include a capping layer. The spacer layer separates the free layer from the pinned layer. The magnetization of the pinned layer is typically fixed by exchange coupling to the conventional AFM layer. More recently, another MR sensor has been developed. For the purposes of this disclosure, the physical structure of this recently developed MR sensor will be called a conventional dual spin valve. The conventional dual spin valve includes a first AFM layer, a pinned layer on the first AFM layer, a first spacer on the first AFM layer, a free layer on the first spacer layer, a second spacer layer on the free layer, a second pinned layer on the second spacer layer, and a second AFM layer on the second pinned layer. The pinned layers and the free layer are still magnetic layers. The magnetization of the first and second pinned layers is fixed by an exchange coupling with the first and second AFM layers, respectively. Because there are more interfaces between the spacer layers and the magnetic (pinned and free) layers, the conventional dual spin valve has more scattering surfaces. As a result, the conventional dual spin valve has a higher MR.
In order to use the conventional spin valve or the conventional dual spin valve as a conventional MR sensor, current is passed through the conventional MR sensor as the MR head is brought in proximity to a recording media. Based on the information stored in the recording media, the magnetization of the free layer can change direction, altering the resistance of the conventional MR sensor. The resistance is low when the magnetizations of the free layer and pinned layers are approximately parallel. The resistance is high when the magnetization of the free layer is approximately antiparallel to the magnetizations of the pinned layers. Thus, the conventional MR sensor can be used to read the data stored by the recording media.
Conventional spin valves and dual spin valves can be used in two configurations. These configurations are based on the direction in which current is driven through the magnetoresistive sensor. Current can be passed through the conventional spin valve or the conventional dual spin valve within the plane of the layers, otherwise known as a current in plane (“CIP”) configuration. Current can also be driven perpendicular to the layers of the conventional spin valve or the conventional dual spin valve. This is known as a current perpendicular to the plane (“CPP”) configuration. For both the CIP and CPP configurations, the resistance is low when the magnetizations of the free layer and pinned layers are approximately parallel and high when the magnetization of the free layer is approximately antiparallel to the magnetizations of the pinned layers.
Although both configurations provide a signal based on the MR of the conventional spin valve or the conventional dual spin valve, each configuration has its drawbacks. The signal provided by a conventional MR sensor is proportional to the sheet resistance of the sensor, proportional to the MR of the sensor, and proportional to the read track width of the sensor. The MR of the sensor is defined as the change in resistance due to the change in magnetization divided by the resistance (ΔR/R). The read track width of the sensor is typically the length of the sensor. The CIP configuration has a higher overall sheet resistance than the CPP configuration. However, the CPP configuration has a higher MR than the CIP configuration. Furthermore, as magnetic recording technology progresses to higher densities, the read track width may decrease, further reducing the signal from the conventional sensor used in the CIP configuration.
Accordingly, what is needed is a system and method for providing a MR sensor having a higher signal. It would also be desirable for the MR sensor to provide a signal which is less dependent upon the read track width of the sensor. The present invention addresses such a need.